1. Field of the Invention
This invention relates to an internal combustion engine exhaust treatment apparatus and, in particular, to a fuel fired burner for heating an exhaust gas stream.
2. Description of the Relevant Art
Advancement in emission technologies for internal combustion engines have resulted in significantly lowered total engine emissions. In general, automotive emissions applications employ an exhaust mounted catalytic treatment device for reducing regulated exhaust constituents such as Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NO.sub.x) in the engine exhaust prior to its release to the atmosphere.
The catalyst treatment devices, or catalytic converters, rely on the latent heat of the exhaust gas to become catalytically active following a cold start. Initiation of catalyst activity occurs at the light-off temperature and is typically in the area of 400 degrees C. A vehicle may require 75-100 seconds or more before the engine exhaust supplies sufficient heat to reach catalyst light-off. The need for early supplemental heat at the catalytic converter prior to efficient emission conversion suggests that significant vehicle tailpipe emissions of regulated constituents occur prior to converter light-off. Accordingly, in order to reduce cold-start emissions, it is desirable to provide an additional heat source at, or before, engine start-up, which will promote faster heating of the converter and, therefore, a shorter time to optimal catalyst efficiency.
Several technologies have been considered for the preheating of catalytic converters. Electrically heated converters, which use an engine driven electrical system to heat elements in the converter, or the catalyst support itself in the case of metal supports, have been proposed. The heat output of the electrically heated units is directly related to the electrical input. In order to achieve the desired, rapid heating of the catalyst support, significant power must be supplied by the electrical system.
Burner systems, to which the present invention is directed, have also been considered for achieving rapid heating. Although not suffering from the drawbacks of electrically heated units, such systems require a burner, a fuel system, and an ignition system along with the related complexity and packaging problems associated with such systems. In addition, rapid, reliable ignition of the burner, burner control, and adequate mixing of the burner output with the engine exhaust have historically been problematic.